I. Field of the Invention
The present invention is directed to methods for forming permanent magnetic bodies, and in particular, bodies incorporating Fe-B-R-T alloy powders.
II. Description of the Prior Art
Fe-B-R-T alloys constitute a known class of alloys formed from varying proportions of iron (Fe), boron (B), one or more rare earth elements (R), and one or more transition elements or related elements (T). With respect to this class of alloys, "rare earth elements" is recognized to include yttrium, scandium, lanthanum, and the rare earths in the lanthanoid series, as well as useful or potentially useful mixtures of them, such as didymium and misch metal. "Transition elements or related elements" is recognized to include not only the transition elements (the metals of families IB and IIIB through VIIIB, inclusive), but also certain nontransition elements located in the periodic table near the light transition elements, which are useful or potentially useful in replacement of or in combination with transition elements in Fe-B-R-T alloys. These related elements include (but are not limited to) zinc, gallium, aluminum, and silicon.
When appropriately prepared, Fe-B-R-T alloys possess permanent magnetic properties which have been found to be useful for a variety of purposes. Most notably, when pulverized to acceptable powder size, anisotropic Fe-B-R-T alloy powders are particularly useful in the formation of composite magnets of various unique and complicated forms. In one method for the manufacture of such composite magnets, the alloy powders are mixed with an organic polymer or plastic (either thermosetting or thermoplastic, commonly epoxy resin) or metal solder, and thereafter aligned and pressed to form a matrix magnet. In an alternative method (impregnation), the alloy powders are first pressed into a desired form and sintered, and a cureable resin is then introduced under high pressure into the spaces or interstices between the sintered powder particles.
Fe-B-R-T alloys can be manufactured in gross by several known techniques, for example, by the vacuum casting or die-upset billet techniques. However, the use of such alloys has in practice been subject to the disadvantage that cast or die-upset billets of Fe-B-R-T alloys are extremely difficult to mechanically pulverize. When mechanically crushed with devices such as disk mills or hammer mills, these alloys are found to be very hard to cleave along the "a" axis or grain boundaries. Crushing yields slivers of alloy material that may be 100 micrometers in thickness yet one-quarter inch in diameter. Conventional mechanical crushing processors or devices typically yield only one to two pounds of powdered alloy per hour of treatment for small units. The effort and cost of powdering the alloy significantly increases the cost of manufacturing the matrix or composite magnets desired.
While other methods of pulverizing iron alloys are known, the application of such methods to Fe-B-R-T alloys appears to encounter other drawbacks. For example, it has been possible to decrepitate and pulverize Fe-B-R and R-T (for example, samarium-cobalt) alloys by sequential hydriding. Such decrepitation has generally been carried out at hydrogen pressures of either a few tenths of an atmosphere or greater than one atmosphere, most often significantly greater than one atmosphere. Previous attempts to employ such methods to pulverize Fe-B-R-T alloys have encountered the disadvantage that the treated alloys have suffered an unacceptable decrease in their room temperature intrinsic magnetic coercivity (H.sub.ci) after saturation magnetization. Applicant does not believe any of such previous attempts constitute prior art with respect to the present invention; in any event, however, composite or matrix magnets incorporating Fe-B-R-T alloy powders formed by such prior attempts have not possessed magnetic properties adequate for their intended use.
Fe-B-R-T powders have also been formed by melt-quenching of the alloy. The melt-quenching process, however, forms isotropic powders, rather than anisotropic powders as achieved with the die-upset process. Composite magnets manufactured from melt-quench powders therefore have magnetic properties inferior to those manufactured from die-upset alloy powders.